Without limiting the scope of the invention, its background is described in connection with the patterning of a photolithographic emulsion for the fabrication of electronic devices for use in large scale integration, as an example.
Heretofore, in this field, photolithographic patterning of integrated circuits has depended on the formation and images with visible or ultraviolet light in a photoresist. To achieve large scale integration of electronic circuit devices, photoresist is patterned is currently achieved using proximity or projection printing. Proximity or projection printing of photolithographic patterns on substrates such as single grain silicon, depend on the printing of a lithographic mask on, e.g., fused-silica.
One problem with photolithographic masks is the degradation of the mask with each exposure to high intensity light or other rays. For example, a fused-silica mask that is used to pattern a large, dense semiconductor chip can have a useful life as low as two hours. Furthermore, the formation of masks requires a separate process, akin to wafer fabrication, in which the masks are patterned on a ultraviolet transparent material, usually having a metallic overcoat into which the pattern is etched. The entire mask producing process is akin to wafer fabrication in that similar care must be taken to prevent contamination with particulate matter from processing reagents and the atmosphere in which the masks are created and handled. The mask process is also very costly, cost which is further accentuated by the difficulty in making reliable, long lasting masks. Also, the turnaround time for mask making makes rapid changes to designs somewhat prohibitive.
A number of problems are encountered using masks for a wide variety of applications. For example, U.S. Pat. No. 5,626,784, issued to Simons, discloses a method for improving the alignment of photolithographic masks using a frame having sides that are individually thermally expandable. The mask is fabricated to be undersized so that the distance between fiducials on the mask is less than a desired distance, which may be the distance between corresponding fiducials on the workpiece. The mask is mounted on the frame, and at least one side of the frame is heated to expand the side and stretch the mask to achieve the desired interfiducial distance. While alignment of a mask is improved using the method disclosed, masks for each of the steps requiring photoresist are still required. Also, with each step requiring a mask, the above method has to be repeated to accomplish the underlying photoresist patterning.